Navigational instrument



March 20, 1945- H, W SLAUSQN y 2,371,714

NAVIGATIONAL INSTRUMENT Filed Dec. 27, 1941 3 Sheets-Sheet 1 INVENTOR HHROLD W61. w50/v mln. l

ATTORNEY March 20, 1945.

w. SLAUSON NAVIGATIONAL INSTRUMENT Filed Dec. V27, 1941 3 Sheets-Sheet z ATTOR-NEY Mar'ch 2o, v1945. H, W SLAUSON 2,371,714

NAVIGATIONAL INSTRUMENT Filed Dec. 27, 1941 3 Sheets-Sheet 3 INVENTOR HHRo/.D W 51.4050,

BY mmm ATTORNEY Patented Mar. 20, 1945 UNITED STATES. PATENT OFFICE NAVIGATIONAL INSTRUMENT Harold W. Slauson, Scarsdale, N. Y. Application December 27, 1941, Serial No. 424,579

3 Claims.

This invention relates to navigational or similar instruments such as those possibly usedf for surveying or map-making. More particularly it relates to mechanical aids for taking Vcompass deviation into consideration.

When afloat, the navigator of a vessel has to consider (l) variation which is the effect on the compass needle of the everchanging magnetic north pole, and (2) deviation which is the eiect on the compass needle of changing magnetic conditions on the vessel itself.` Variation is` a term applied to changing magnetic conditionsoutside of or beyond the vessel while deviation is a term applied to changing magnetic conditions on the vessel itself. The rate of vari-ation, and its direction, is marked in association with compass roses on government charts, whereas the deviation vfor each particular vessel must be determined from time to time. The degree or extent, as well as the direction of deviation is usually different with each compass degree, so that a good navigator checks his compass every so often by swinging ship" or other means and tabulates the degree and direction of deviation of his comto be steered coincident with the laying of that course, whereupon by simple addition or subtraction, the true course can be determined. Another object of this invention is to devise a. compound apparatus or instrument from which not only the deviation can be readily and unmistakably determined but which will also take into consideration the variation. Since deviation is more unstable than variation, due to changing conditions on the vessel, a further object of this invention is to devise the deviation indicating instrument so as to be readily adjustable to meet or compensate for changed deviation causing condition. And a stil1 further object is to devise a deviation indicating instrument that can be used to go from chart to compass or Afrom compass to chart, the latter being necessary when taking bearings with the vessel as the base.

With these. and other objects in view, one

i'eahueoftheinventionmaybesaidtoreside ingo the combination of a compass rose marked on a disc, that is, the disc has marked on or near its periphery, 360 degrees of arc. Associated with the disc held thereon in a temporarily iixed po.

sition and relationship by a scale-bearing cover plate is a face on whichhas been made-a camshaped graph that portrays the deviation data from chart to compass deduced from swinging thev ship. And the card may. contain a second similar cam-shaped graph that portrays deviation data from 'compass to chart. A further and supplemental feature of the invention is the provision of a chart-holding board having a pivoted arm that supports the above described disc and card, so arranged that the variation can be compensated for by the adjusted angle at which the Y sembly, although with sections broken away, that embodies the deviation indicating feature of my invention. j

Figure 2 is a vertical sectional view taken along the line 2--2 of Fig. 1.

Figure 3 shows a top plan view of the disc that is adapted to hold the deviation card, while Figure 4 is a top plan view of a deviation card adapted to be associated with the disc of Figure 3.

Figure 5 is an enlarged sectional isometric view of a part of the disc, its card and its cover plate. y Figure 6 is a plan view of a complete chartholding board and a pivoted arm carrying the disc and its associated parts.

Fig. 'I shows a plan view of the baseboard lil with its associated equipment.

Fig. 8 shows a front-edge view of the parta of Fig. 7 looking from bottom to top of that figure-however, the plate in the center of the figure with its knurled nut,l84 is' open or thrown x rig. 12 is an isometric view of. the board' m and those associated parts not removable therefrom; while in degrees. of arc through 360.-

Fig. 13 shows a similar view of the removable parts.

' Fig. 14 is a partial sectional View of a detail of the cruciform member I2! shown at the left of Fig. 6.

In the drawings, the numeral II indicates a disc assembly including the disc marked on its annular rim section I2 adjacent to its vperiphery i3 indicates a recessed central section, and Id a central round aperture. The bottom of the recess I3 preferably is of` transparent material I5 marked with right angled lines I that correspond to parallels` of longitude and latitude on a chart. This bottom I5 may be held in association with the rim I2 of the disc II l by a further bottom element I', also elled edge di. Then from the data learned by swinging ship, it will be found, say, that the compass has an easterly deviation of degrees.

pencilleddot is placed on the card 30 through the transparent. Il indicates a plate that fits on top I of the disc II and which is apertured by a rectangular opening at It. I9 represents a knob having a screw threaded bottom recess I that co-acts with a screw threaded boss 2l on a boltlike element 22 for holding the disc EI and its associated parts together. It has a disc-like base 23, a cylindrical section 2Q that is complementary with round aperture It on the disc assembly II, a squared section 25 that is complementary to rectangular aperture I of the plate II, and the threaded boss 2l that enters the knob I9. 50 indicates a face or card or disc of paper, wood, plastic or metal of a size and thickness capable of being seated in the recess I3 of the disc as-` sembly II. It is provided with peripheral tabs 3l adapted to enter the cusps 32 on the inner edge of the rim I2 of disc II, for holding the card securely against any relative rotational displacement between disc II and card 30. The card has a central round aperture 33 similar in size to aperture I on the bottom I5,since both bottoms I5 and it, as well as card must t over cylindrical section 26 of the bolt-like element 22 for rotational movement thereon. f 35 indicates a chartto-compass deviation graph on card 30 hereinafter describedY while 36 indicates acompass-tochart deviation graph on the card 30, also to be described. The latter is vshown in red orin dot and dash lines for more easy identiilcation so asr` tive numerals appear on both sides-of a zero mark 43. The zero mark extends as a circular line on the plate, on the outer side of whichA appears some indicating legend 44 as a plus sign to indicate west, while within the circular'lineV appears a corresponding but .complementary legend 45 such as a. minus sign for east. 46 indicates a c'utaway portion on the mob I9 so as not to. obscure the slot v4I). I, Y

The cam-shaped graph. on card 3|! is prepared as follows: The device is assembled in the arrangement shown but with a blank card 3B iitted into the recess 'I3 of the disc II, with tabs .3| of the card neatly tted'into thecusps 32 of the disc II. The plate I'I is then emplaced and the' knob I9 put on to hold the parts inplace, but

`disc is turned to, say, 40.

slot 40 opposite minus 5 on the scale 4t2. Then, the disc Il is rotated to bring, say, 20 in alignment with the bevelled edge. Data from swinging' ship will show that the deviation for 20 is, say, minus 2. Whereupon another pencilled dot is placed at that point on the card. Next, the Data shows that at this heading, the deviation is 0. Another pencilled dot is applied `to the card. And so on through as many headings as data was taken for in swinging ship. Then the plateil is removed to expose the card lt0, whereupon the pencilled dots are connected into a graph that takes generally the form ofthe contour of a cam, and thus the graph 35 is formed, or data may be obtained at any time on any course on which the compass heading may be compared with the charted course. A Y

The graph 36 is made by this same method except that diiierent readings and data are used.

They may be obtained from a Napier diagram,

a sine curve, or by trial and error. In thiscase, the disc II has its zero degree mark aligned`with the bevelled edge di. Then the data'obtained from swinging ship is observed toV iind from the deviation reading of Zero, what is the true reading. This is just the reverse of the iigures used the knob is not screwedup so tightly but what Y the disc II can be rotated without rotating the card 32. The disc II is rotatedto bring the uro to make the chart to compass graph. Suppose that the data shows that when the, deviation reading is 0, the true reading is 5 degrees westerly or plus. A pencilled dot is then applied to the card opposite plus 5 on the scale d2. The disc II is then moved to a reading 10 or 20 degrees away from 0 and the procedure is followed again, using deviation to true instead of true to deviation as in the chart-to-compass graph. When enough dots have been accumulated, the plate II is removed to give access to the card 30 -whereupon the dots are connected by a dot and dash line to form graph 36 which is the compass to chart graph. Chart-to-compass graph 35 is when taking bearings from the vessel.A

. Assume now that the graphs have been properly made on the card 30 and the parts have all been assembled as shown. Then suppose that the navigator determines from the government chart that he wants to steer a true course of 0 (after havingA corrected for variation). He turns the parts of the device as shown in Fig. 1 with the bevelled edge 42 aligned with 0 on tikti disc. The navigator. then looks down the slotr'lIIl to see where the graph35 appears through the slot 40 and particularly where it intersects the scale 42. `In Fig. 1 he will see that it intersects the scale at a marking on minus 5. Therefore, he will then move the disc I I to the left until the bevelled edge is aligned with 0 less 5, namely, 355 and vthat will be the compass course to be steered to equal the true course of 0. Assume, now that the course isvto be changed and from the chart, the navigator determines that the true course he wants to follow is Hefthen moves disc 'Il as showx in Fig. 5 to align 90 on the disc scale with the bevelled edge of the slot 40. -Next, he looks down'the slot until he encounters the graph 35 and observes that it intersects the scale 42 at' plus 5. The operator thn may move disc II to the right until 90 plus 5 or 95 is aligned with the degree 'mark into radial alignment with the bev- 7 bevelled edge, whereupon he will know that he should steer a compass course of 95 to have his vessel proceed on a 90 true course. However, it is preferable to leave the edge on true (or magnetic) course and to make mental calculation from the slot without moving the card so that V the latter can alwaysy show the line-of-course or Objective on chart;

when taking s bearing from the ship,`1et us y say that by the vessels compass, the object bears The navigator turns the parts as shown in Fig. 1, whereupon by glancing down the slot 40 until the compass-to-chart graph 35 is encounered, he sees that that line intersects the scale 42 at plus 5. Then he turns the disc to 0 plus l chart and therefore it functions, at least in part,

as the support for the other parts. The disc (with its card 30) is rotatably mounted on the cylindrical section 2l of the base 23 while the plate |1 is non-rotatably mounted on the squared section I8. The knob I9 is in effect a clamping means to hold the parts in non-rotational assembly when the knpb is tightened, but when loosened, the disc |I and its card 30 can be readily rotated as a unit.

The device of Figs. 1 to 5 is only capable of indicating changes to compensate for deviational errors. When it is used, variational errors must be calculated and allowed for. However, in the apparatus shown in the remaining figures, the variational errors can also be compensated for.

In Figures 6, '1, et seq., there is shown a small substantially rectangular baseboard ||0 that is longer than wide and that is not nearly so large as even the folded size of a chart. Its size is merely sufficient to receive the instrument completely folded thereon. It may be made of suitable ply board, plastic composition, or the like, is preferably substantially rectangular' and carries attached along its upper edge an arrangement generically indicated by H, hereinafter more fully described, adapted to hold in position a chart which may have been slipped beneath the clamps before the nuts are tightened if desired. The chart folded to about one-fourth of its full size is shown at H1.

The apparatus also comprises a substantially universal parallel motion mechanism including the plate |1 carried by the parallel arms ||9 attached thereto at pivot points |20; the cruciform member |2| carrying the pivots |22 for the opposite ends of the arms H9 spaced apart the same distance as the pivots |20. On an axis at right angles to that passing through the pivots |22 and below the same are mountedthe pivots |24 for one end of av pair of parallel arms |215, extending to the pivots |26 with the same spacing as the pivots |24 on the clamp member |21, comprising a U-shaped device having the top arm, a bottom arm and a connecting member. The bottom arm is received against the underside of the baseboard H0, the member againstits edge, while the upper arm extends over the upper surface of the base and carries a pair of clamp screws IJI adapted to be manipulated .by the knurled heads |32 to secure the clamp rmly to the base in any desired position along'its edges.

The parallel motion mechanism just described permits the plate I1 to be moved over a definite area of chart always parallel to its initial position, thereby offering means for determining the angularity of a course on the chart in respect to the true meridian as indicated by any of the longitude lines |34 on the chart or for that matter to the latitude lines or parallels |25. s

To permit this the plate |1 has pivotally secured beneath it the graduated disc or protractor that simulates the compass rose on the chart, except that the graduations I2 on this disc are preferably arranged counterclockwise from zero to 360 and cooperate with index mark 42 arranged on inclined surface 4| on the plate l1. These index marks correspond respectively with indicia representing the cardinal compass points north, east. south Vand west.

The pivoting of the disc to the plate |1 is accomplished as hereinbefore described. The knob I9 provides a convenient operating handle for moving the instrument over the surface of the chart and at the same time permits locking of the disc at the desired angle in respect to the plate.

The disc vcarries preferably integral therewith the ruler, straight-edge or scale |05, the upper marking edge 5| of which is parallel to the zero-180 diameter` of the graduated disc.

This edge, as well as the opposite edge |52, may conveniently be graduated to any suitable scale to replace the usual dividers resorted to for trans, ferring distances to a scale. It may have the usual inch marks with suitable intermediate graduations, or it may have engraved thereon a scale of miles either nautical or statute, preferably in one or more of the ratios used on most charts, for instance 1 to 80,000.

The construction of the apparatus is such that the scale |50 has its upper edge preferably tan- 40 gential to the periphery of the attached protractor or disc |I. Because of the vertical offset |53 in the plate l1, the arms il! may move above the scale and it is permitted to rotate through a full 360 without interference with any of the parts of the mechanism carrying the same.

The `arms carrying the pivots |22 on the cruciform member |2| are offset upwardly to permit the parallel links ||9 to move above the parallel links |25 when necessary so that there is no interference between the same. This arrangement of parts permits the apparatus to be folded into a compact assembly with the scale substantially parallel to the arms ||9 and with them overlapping the arms |25. In order that the clamp, |21 may be'attached to the baseboard H0 when lthe apparatus is folded for packing, one corner of the baseboard is clipped at the angle shown at |55 which accommodates the -clamp |21 when the apparatus is compacted.

The clipped portion |55 is longer than the length of the clamp. |21, and is designed so that when in the folded position, the clamp |21 lies wholly within the rectangular contour lines of the base ||0. (See my Patent No. 2,223,428.)

The navigational chart ||1, preferably in folded condition, is held in association with the baseboard ||0 by an arrangement or assembly, shown collectively at H that has certain essential functions which can'wbe carried out,`for example, by the construction shown, wherein the baseboard ||0 has rigidly fixed to the under side thereof, a channel |55` (see Figs. 12 and 9) that has less length than the baseboard ||l. It is provided with ears |51 and v|55 projecting inwardly over the baseboard and each is provided with an aperture l5@ and |88 respectively. The baseboard is provided with holes itl and |82 arranged in vertical register with the apertures |59 and |89 respectively, so that a pin |53 that has arrenlarged head or bent-over handle may pass through aligned la'perture l5@ and hole lll. A similar headedV pin llil passes through aperture le@ and hole |62.

Arranged for disposition in adjustable rela-- tionship with theehannel ltlt, is chart-carrying member or carrier C, substantially U-shaped in cross-section (Fig. i3) having a bottom flange it@ and a toplange itl', with the latter of less length than the carrier body C or its bottom flange i665. The body portion oithe'carrier C terminates in solid horn-ends |68 and it@ respectively, thatare of less depth than the depth 0f thecarrier C so that a slot il@ is provided between the bottom of the horn-end and the bottom flange i558 of the carrier, so that the chart lll, even when folded will pass through the slot-s llll. A hole lll passes through the horn-end |58 that isaligned with an apertureA ll? in the bottom flange itil through which pin it can pass when it also passes through aligned apertures |59 and ltl of the channel l58 (Fig. 8). Similarly, the horn-end |89 has a hole llt that is aligned with aperture lll in the bottom flange It@ oi the channel ltf'so that when the carrier is in secured position with the channel |88, pin |66 passes through not only the hole H3 and aperture lll but the apertures |68 and |62 of .the channel |56.

The top flange |67 of the carrier C is provided with a plurality of clamping members or clamps ll vertically adjustable to and from clamping position against the bottom flange It, by means of headed adjusting screws |16. The channel |58 is provided with a hinged clamping bent nger lll, and also with a plate |18 hinged to the channel. Projecting from the plate |18 is a. threaded pin |19 that has associated with it a knurled nut |88. Adapted to be clamped between the'plate |'l8 and the knurlednut |88 is a guide member |8l having a slot |82 through which the knurled pin |19 passes. At a free end of the to the chart carrier C by means of the screw operated clamps lle and ll@ to hold the chart rlrmly to the bottom flange l@ of the carrier C. After observing that it is, say, westerly variation that is to be compensated for, the left hand edge of the chart, either open or folded, should not extend far enough beyond the left hand end of the carrier to interfere with the clamp l2?! and its parallel arms S25. Suppose new from observing the compass rose nearest to the course to be steered, the variation is shown to be 9 west. Pin

moved and the carrier with its chart is swung about the left hand pin ld vas a pivot until the pointer le@ at the right end of the carrier C reaches 9 on the westerly variation scale 669. Thereupon the carrier is xed in this adjusted position by centering the dowel-shaped pins lil@ in the holes l8l in thev top iiange of the carrier C (Fig. 6) whereupon the slotted guide lill is clamped by nuts it@ and l8l to hold the parts in the relationship shown. Thereafter, the course can be plotted as magnetic, or compass with 0 deviation, for Variation is thus completely compehsated for.

If the variation is easterly, the arrangement is reversed, in that left hand pin |66 is removed and the carrier C with its chart is swung about right hand pin i825 as a pivot until the pointer l9| on the left end of the carrier points to the number of degrees on the easterly variation scale |88 that the compass rose shows to be the variationof the area passed through by the course .t0 b'e steered. Such an easterly variation'compensating position is shown by the dotted lines in Fig. 6.- When easterly variation is to be compensated for, the right hand edge of the chart guide 8l and alsol passing through the slot |82,

is a threaded pin |83 having a knurled nut |86. On` the other end'of the pin |83 from the nut lill, is a small plate |85 provided .withone or more projecting dowel-shaped pins |86. These dowellike pinsA |85 are adapted to fit slidingly into holes |81 in the top ange of. thecarrier C, under certain conditions.-

Adjacent-,the left hand side of the baseboard H8, is a scale |88 'preferably of some bright color such as red.` The right hand edge of the scale is curved on a radius swung from the pin |63. The scale is marked. in degrees of easterly `variation. A similar scale |89 is provided at the right hand .of the baseboard ||0 in some other bright color-,such as green, and its left hand edge is curved on aeradius' swung from pin |64. This scale is marked in degrees ofwesterly variation.

If easterly variation is to be compensated'for, the

left hand -pin 8,4 is removed and thecarrier, with its chart, is swung about rignt'nand pin lss as j .a.plvot. For that reason pin` |63 may well be colored to match the color of the easterly variation scale |88, whereas pin |84 can be colored to match the westerlyvariation scale |88.y The ears |58l and |81 may also -be, similarlycolored so that no mistake is made as to which pin affects which .In mechanical operation, the chart is clamped 'l5 should not extend substantially beyond the right hand end of the carrier C, and to make this possible, the clamp |2'l with its parallel arms is shifted from the upper left corner of the baseboard lll) to the upper right hand corner. When the carrier is to be returned to normal or unused position, it can be clamped so, by pivotally moving or swinging the spring finger Ill over the carrier, as shown in Figs. 7 and 8, and of course. the previously removed pin is restored to normal position. In order to permit the reversal of position of the clampI |21 with its parallel arms |25 and I9, there must be a reversal of the direction in which they are. attached to the cruciform member 2|. To that end, Fig. 14 shows how the parts may be readily dis-assembled by removing the pivot ,screws |22, and the'pivot screws replaced when the parts are reassembled to maintain them |63 at the right hand of the assembly H is reby the clamp 21 and its rearranged parallel arms |25 and ||9 is shown also in dotted' lines in Fig. 6..

Invv practical operation, the operatory observes from his chart the variation of the compass in that general area of the chart through which the vessels course transits, especially as to whether it is easterly or Westerly. Next, the oper'ator clamps the chart in the carrier C by westerly, then the chart is extended through the right hand slot as can-.be seen in Fig. 6. The

righthand pin |63 is removed and the carrier'v isthen lswung about pin |64 as a. pivot, until'n .l the pointer |98 vat the right end of the carrier C points to the number of degrees 0n the 'scale-|88 of the" that are equal to vthe degrees and their subdivisions that are indicated onthe compass rose.

positioning can be done readily by means of the parallel arms |25 and H9. Next, the operator observes through the slot 40 of the deviation compensator plate I1 that part of the graph 35 on card 30 that shows through the slot, how

many degrees, and subdivisions thereof, if any,

the exposedfportion ofthe graph is above the deviation line 43 marked on the plate |1. This numberof degrees and possibly fractions thereof, are then added by the operator to the number of degrees'on the 'scale I2 on disc that is aligned with edge 4| of the beveled edge of the plate |1-the sum being the compass course to be steered with both variables of variation and deviation being compensated for.

Suppose now that wherrrunning the charted course, the operator` wants to take a bearing on some iixed object. He ips upA the dowel-like pins |86 out of holes |81 in the carrier C and pivots'the slotted guide |8| about its horizontal Divot to aposition free and clear of the chart. The carrier C with its chart still clamped in place, is swung back linto normal position, as shown in Fig. 7, and the spring nger |11 flipped over it to hold it in this normal position'. A

compass bearing is then taken Pon the object."

y |8 until its dowel pins slip'in'to the holes |81, and the parts are ready for further use in com- `pass-to-chart relationship, whereupon the operator can then see the relation of his course to that object. In other words, when using chartto-compass relationship, the carrier C with its chart is adjusted as shown for instance in Fig. 6, whereas when using compass-to-chart relationship, thel carrier C and its chart is' adjusted as shown in Fig. 7. That is, the chart is at the variation angle to the baseboard, I0 for running a course, whereas for taking bearingsythe chart is straight with the board vand itsme' ilians are at 90 angle with' the top edge of the aseboard. Since the magnetic course is really" deviation 'from the compass reading, the disc is used to give the magnetic course. And.Y as the chart itseli'is adjusted`to compensate for the variation,

the reading of thedisc llas used' in my total combination, shows directly the true course.

Thejpins |83'and |04 must be removed and replace 'as is appropriate to the'desired position er C to the channel\|58. The-changing oi' the clamp" |21 with its parallel arms |25 and I0, as well.asits disc andthe straight edge or ruler, from the left hand side of the baseboard I I0 to the right hand when easterly variation is to be compensated for (rather than westerly variation as shown in Fig. 6) because it will be easier to handle, for otherwise, in the left hand position, the operator is manipulating the apparatus away from the radius of action instead of into it.

The apparatus that embodies this invention has many advantages. It is small, neat and compact. Because of. its capabilities, the chart can be folded when applied in position in it, as much as one-fourth the normal extent of the chart.

'- Such compactness is highly desirable on small remains visibly indicated in the apparatus, even though both compass and chart should be moved to another part of the boat. 'I'he instrument shows all that the operator needs to know. And finally, the instrument can be stowed readily on the smallest vessels.

Naturally, the invention is capable of other embodiments than the vone shown, so the criterion of what comprises my invention is that which falls within the ambit of the appended claims, using, of course, the rules about equivalents and about reversal of parts.

For instance, instead of using the card 30 as made of paper, I contemplate that it may be of a material that presents a facesuriace or portion on which the data portraying graphs 35 and 36 may be readily erased or deleted. After such deletion, the surface or face is such that the operator can readily write in a new graph without the necessity of substituting one card for another in the disc assembly Therefore, the erasibility of a graph from the card or its equivaient surface, and the ready drawing in of a new graph, is a part of my concept of this invention.

Still another such modiiied embodiment that is still within my concept of this invention, is that the disc assembly may be sold and used when provided with the ruler or straight-edge |50 in therelationship shown in Fig. 6, but removed from the parallel supporting arms ||9 and |25. In other words, it is entirely possible to use as an independent deviation compensating device, the

'arms and the deviation compensating device to the particular baseboard shown herein to lbe my preferred embodiment, the deviation compensating device could, of course, be clamped or otherfastened to a full sized chart table, such as is used on ocean going or other commercial vessels. l

The devicesf this invention may, of course, be

, used on airplanes.

I claim:

l. Apparatus of the class described which comprises an apertured bottom sheet, an annular scale associated therewith marked in 360 otan arc, an apertured platev whose aperture is aligned with the aperture of the bottom sheet 'and presentingA a radially-extending edge bearing scale markings, and means for clamping the foregoing parts together, characterized by an apertured annular card bearing two graphs of which one indicates a value extending for its major portion on one side of the aperture of the card While the major portion of the other indicates an opposite value extending on a. substantially opposite side of that aperture, means for securing the card and scale in adjusted relationship, and two groups of lines marked on the sheet with the lines of one group extending at right angles to `those of the other group.

2. Apparatus of the class described which. comprises a sheet having seele markings on its nea ripheral section, an apertured plate member hav ing scale markings thereon along a line .radial esima thereof, an apertured cerd arranged concentric with the disc bearing on its face curving graphs of which one extending for its major part on. one side of the aperture oi the 4card indicates one value While the mejor portion of the other extending on a substantially opposite side of the aperture indicates an opposite value, means or securing the sheet and card together; and meens for securing the plate and the card as well as the sheet together for relative movement therebetween.

V3. Apparatus according to claim 2 with the addition of right-angled markings associated with the scale markings of the sheet. y

HAROLD W. SLAUSON. 

